(1) Field of the Invention
The present invention relates to the opening and closing a fluid conduit having a large cross section. More particularly, the present invention relates to an apparatus for opening and closing a downcomer conduit that directs crude gas from a blast furnace in a generally vertical direction into a "dust bag" which removes particulate matter from the crude gas. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
In the manufacture of steel, crude gas exiting the top of a blast furnace is directed through a collector pipe to an enclosure which is known in the industry as a "dust bag". The crude gas comprises a mixture of gas, steam and particles of dust having varying size, the gas being released at a relatively high pressure and temperature from the blast furnace. The "dust bag" functions to remove particulate matter from the crude gas. in many steel manufacturing processes, a collector pipe, known in the art as a "downcomer", extends in a generally vertical direction to a dust bag which is situated downstream of the blast furnace, the diameter of the dust bag being, in general, greater than the diameter of the collector pipe. In the case of a blast furnace, it is often necessary to rapidly isolate the dust bag from the blast furnace. Thus, near the junction of the collector pipe and the dust bag, the collector pipe includes a valve for opening and closing the pipe. The conventional pipes, in general, include a transverse slit which provides for the insertion and withdrawal of a shut-off plate so that when the shut-off plate is positioned within the pipe, the pipe is closed. When the shut-off plate is retracted from the pipe, the pipe is opened. One valve for opening and closing a collector pipe is disclosed in German Pat. No. 2,136,216. Among other known valves, the most usual types of valves are "goggle" valves: a plate having an aperture at one end slides horizontally back and forth within the slit in the pipe to open and close the pipe. Another conventional type of valve comprises a simple circular disc or shutter which may be slid horizontally into the pipe.
The aforementioned shut-off valves satisfy the accident prevention requirement that no one may work in a crude gas installation except behind a full joint, that is, the pipe must be completely cut in the transverse direction so as to minimize or eliminate the risk of gas leaking from the furnace to an area near the person working. However, in the case of collector pipes functioning under high pressure and high temperatures, such as that present in blast furnace crude gas, the aforementioned valves fail to sufficiently seal the collector pipe with respect to the environment external to the pipe. During movement of the valve plate to either open or close the valve, it is difficult or impossible to prevent appreciable leakage of crude gas to the external environment. The conventional solution to this problem is to provide a hermetically tight armoring completely surrounding the valve and its accessories in order to insure hermetic sealing from the inside of the pipe to the external environment and between the upstream and downstream portions of the pipe.
Although the prior art armoring has solved the hermetic sealing problem, the armoring has, in turn, given rise to further problems. In the case of pipes having a large cross section and being exposed to considerable pressures, as occurs in crude gas collecting pipes in modern blast furnaces, the weight and space required by the armoring is relatively large. Since the armoring must surround the entire valve and enable the valve to perform the sliding movement perpendicular to the pipe, a cumbersome and expensive superstructure is required. A tendency in steel manufacturing is to operate at increasingly high pressures, and the foregoing problem becomes aggravated as pressure increases. As the armoring must be made correspondingly strong and robust, a further increase in weight and size is necessary. It is not unusual for the entire structure to weigh tens of thousands of kilograms.
It is an object of the present invention to provide an apparatus for opening and closing a collector pipe of wide cross section of the type which has a relatively low total weight.
It is another object of the present invention to provide an apparatus for opening and closing a collector pipe wherein the space occupied and the total weight of the superstructure necessary to support the valve is reduced considerably while at the same time insuring hermetic sealing.